Stress Calculations *HELP!!!*

[Ritch7]

hey everyone!

 

major rush job has just been hit on me, that yes as you have guessed has me working on a saturday night from home.

 

no probs for me, but im dealing with stress calculations and to be honest i don't have a clue this is not my feild at all.

 

the guy who normally does it at my work has been on holiday since tuesday, and its been thrown at me.. now.. i cant beleive it!!!

 

 

to cut along story short from the notes does any one of you knowledgable people know what these soultions are, i have been given the calcuations that need to be done by a collegue but neither him or me know how do them.. can someone please help...!??

 

i have put the 2 problems in a word doc because i dont know how to type the smalled squared symbol and with the divide lines.

 

im sure its really simple but i just dont know, i have attached the 2 question calculations.

 

all the thanks in the world if someone knows... im a complete standstill!! thank you so much in advance

 

Ritch

2 Questions.doc

[dbroada]

the biggest problem you have there is not knowing (giving) the units. If you had them a lot of the confusion would probably drop out. It is simple just to do this on a calculator but I really don't think all the information is there. If you are to do what you have in front of you you have...

 

584 * 4.787 divide by

87000000*0.075*0.075*0.075*0.075

 

and

 

the second one doesn't really make sense but I read it as the cube root of the quadratic root of 1.29 but I'm prepared to be corrected.

[CarlB]

It's not entirely clear as there are no parentheses to make it obvious how it's grouped, but I think it is:

 

(584 x 1 x 4.787)/(87 x 10^6 x 0.075^4)

 

= 2795.61/2752.73 = 1.016

 

Second equation. which reads the cube root of 1.29 raised to the power of negative 4:

 

(1.29^-4)^1/3

 

= 0.712

[dbroada]

I stand corrected

[Ritch7]

wow guys u dont know how much that means, this has officially been the most stressful night off my life, ive been on the phone to so many people trying to sort this!!!

 

thank you so much i think u 2 have cracked them 2, i have just two problems left now from garys workload (guys whos away)

 

please see attached, this makes no sense to me whatsoever gentemen, the first 1 is out of curiosity i cant see how hes got that answer its similair to the 1.29 prob, and the one below is just as how its on was on his desk with the spaces as i presume have to be filled with formulas??? please see attached.

 

if 1 of you two can sort this im buying you a drink!

 

thanks so much, your'e a life saver and proberly saved my job aswell!

final 2 questions.doc

[CarlB]

Hey Ritch no problem, it's sat morning here in Alaska so brain still working OK

 

first; the cube root of 1.80:

(1.80)^1/3 = 1.212 not 0.564.

However if a decimal wa misplaced, and instead of 1.8 it was supposed to be 0.18; (0.18)^1/3= 0.5646, so maybe it's supposed to be 0.18, or someone entered it wrong in the calculator.

 

Second problem, which I think is :

 

Not sure where you got R=0.2, not mentioned in the "given" data

 

1.13x (PR/FD)^1/2

 

=1.13 [(3.5 x 9.81 x 0.2)/(45 x 10^6 x 0.015)]^1/2

 

=1.13 x (6.867/675000)^1/2

=1.13 x .0032

=0.0036

 

Since input was in Newtons, meters, etc the units for output should be meters.

so, D=0.0036m = 3.6 mm

 

not sure if this is a reasonable answer, if so probably round up to 4 mm

 

hope this helps!

[dbroada]

Carl is obviously much quicker at getting it right than me so hopefully he will be along with an answer but I'll make a couple of comments anyway. In fact he has already posted so shortened version from me......

 

Again, UNITS is everything. Make sure you are consistent all the way through. Don't mix m & mm in the same formula. It is this reason that you may see 10^6, which is 1000000, the conversion required to change m^2 into mm^2

 

Just in case Carl is not used to metric units, 9.81 is the force of gravity, 9.81m/sec^2 or in American, 32ft/s^2. It is used to change weight into a force.

[Ritch7]

Hi Carl/Dave thanks very much, you two sorted the problem for me,

 

man this forum is the best.

 

much appreciation

Ritch